The present invention relates to a fuel supply control system for an engine for motor vehicles.
A system in which the amount of fuel supplied to an engine is calculated based on amount of induced air, speed of engine, and other factors is known.
On the other hand, when the engine speed exceeds a predetermined value, intake and exhaust valves begin to bounce, which will cause misfiring and/or breakdown of the engine. In order to prevent such disadvantages, a fuel control system has a fuel cutoff system which operates when the engine speed exceeds a predetermined fuel cutoff speed which is slightly lower than the bounce beginning speed. However, in an automotive engine having a valve system provided with a hydraulic lash adjuster, if the engine is operated at a low temperature of the lubricating oil in cold engine state, the oil pressure in the hydraulic lash adjuster becomes very high because of high viscosity of the oil. Accordingly, the valves are lifted by the oil against springs, in a middle speed range, thereby holding the valves open. This causes the engine to stall, reduction of the power of the engine and rough idling.
Japanese Patent Application Laid-Open No. 59-208132 discloses a fuel cutoff system operated in which the fuel cutoff engine speed is set to a higher value in accordance with a temperature of coolant detected by a coolant temperature sensor for a set time after the start of an engine. However, since the high fuel cutoff engine speed is set, engine speed may exceed the bounce beginning speed to cause bouncing.